单根DNA短链构筑pH响应超分子水凝胶

p H-Responsive Supramolecular Hydrogel Based on One Short Strand DNA

设计合成了一条包含两段自互补序列和一段富含胞嘧啶(C)序列的DNA单链.在碱性条件下,两段自互补序列可通过分子间自组装形成一维DNA纳米线,调节p H至酸性条件后,胞嘧啶序列通过形成双分子i-motif结构将纳米线交联,从而形成DNA水凝胶.当加入酸或碱调节体系的p H时,水凝胶的力学强度会发生变化.在p H为5.3时,水凝胶力学强度达到最大,增大或减小p H都会使水凝胶强度降低.同时,改变DNA单链浓度也能够调节水凝胶的力学强度.此凝胶制备过程原料合成简便,无需涉及不同DNA链定量配比的问题,大大简化了实验操作;另外i-motif结构在形成与解离两态之间的转换非常迅速,在几秒钟之内便可完成,也赋予该凝胶快速p H响应的特性.

We design a single strand DNA containing two self-complementary sequences and a half i-motif structure. The two self-complementary sequences can self-assemble to form DNA nanowires. Then, the hydrogel can be fo/rmed by crosslinking the half i-motif structures under acid condition. The single strand DNA is diluted to 3 mmol/L in 1 TAE buffer （pH = 7.5） containing 12.5 mmol/L MgClz. The system is heated to 95 ℃ for 5 min and slowly annealed to room temperature. The pH is adjusted to 5.3 to form the DNA hydrogel. The DNA oligomers and assemblies are characterised by PAGE. Then circular dichroism is used to characterize the structure of the duplex and the i-motif. Rheological characterization is used to evaluate the mechanical properties and thermal stability of the hydrogels at different concentration and pH. By changing concentration of the single strand DNA, one can adjust the mechanical strength and thermal stability of the hydrogels. Besides, the mechanical strength can be tuned by changing pH values. When pH value is 5.3, the storage modulus （G＇） of the hydrogel is 243.9 Pa. When the pH value is increased to 6.0, the G＇ is lowered to 225.7 Pa because the stability of the i-motif structure decreases as the pH value increases. However, when pH value is changed to 5, the G＇ is greatly reduced to 57.4 Pa, which is caused by the instability of the duplex structure under acidic condition. In this procedure, the single strand DNA is very easy to be synthesized and the ratio of DNA strands has not to be controlled. Thus, the experimental steps are greatly simplified. Also, the transition of the i-motif between hydrogel formation and its dissociation is reversible and fast （within several seconds）, which makes the DNA hydrogel fast pH responsive. Due to these characteristics, this DNA hydrogel holds great potential in bio-sensing, drug delivery and 3D printing.